Attempts at replacing or rebuilding diseased or damaged structures in the human body go back to 3000 B.C. It was not until the middle of the 1900's, however, that the use of synthetic materials for rebuilding body structures met with widespread and reproducible success. Advances in material science and biomaterials have afforded much of the success. The need for new and better implants exists in every field of medicine in which disease or trauma can be treated surgically.
As technology continues to improve the state of the art, the standards for successful implants continue to improve performance factors such as mechanical properties, bioresorption, biocompatibility and integration into existing tissues. The new research being conducted today on growth factors and cytokines, controlled drug release, and cell-based therapies anticipate a time when implant materials will be expected to promote healing, alter disease process and stimulate tissue regeneration.
The inventors have continued to make improvements to produce good quality cartilage cells in sufficient quantity to be transplanted effectively. The inventors have previously described a microcarrier spinner culture system that facilitated maintenance of chondrocytic phenotype while enhancing proliferation. The chondrocytic phenotype is characterized by expression of collagen type II and a family of high molecular weight, aggregating, sulfate-containing proteoglycans known as aggrecan. This culture system was based on a bioreactor originally designed to grow bacteria in large quantities. Articular and nasal septal chondrocytes have been grown on dextran or Cellagen™ (highly cross linked collagen type I) microcarrier beads under controlled pH, oxygen levels, nutrient supply and mechanical agitation conditions. Under these conditions, fibroblastic chondrocytes, which were originally propagated in traditional monolayer culture began to re-express their chondrocytic phenotype while propagating to 20 times their original number. This represents a great advantage over the traditional static monolayer culture system, which facilitates proliferation but leads to a fibroblastic shift in phenotype. Likewise, it offers an alternative to the battery of three-dimensional gel or scaffold systems, which include agarose or collagen gels, calcium alginate gel, mixed fibrin-alginate gels, three-dimensional meshes of resorbable polymers such as polylactide, and encapsulation in alginate beads. These culture techniques facilitate the maintenance of a chondrocytic phenotype, but are limited in maximizing proliferation.
The inventors have also utilized nasal cartilage as a source of chondrocytes. Like articular cartilage, nasal cartilage is hyaline cartilage, and the chondrocyte is its only cellular component. Nasal cartilage is also readily obtained from nasal septal surgery. The tissue offers a source of normal chondrocytes and provides an alternative model to using chondrocytes of nonhuman origin, immortalized cell lines or human osteoarthritic cartilage, which may not accurately represent normal human chondrocytes.
Improvements of the invention are set forth below and the subject matter of Ser. No. 09/275,319 filed Mar. 24, 1999 and Ser. No. 09/712,662, filed Nov. 14, 2000 are incorporated by reference herein in their entirety.